The present invention relates generally to satellite communication systems, and more specifically, to methods for testing multibeam satellite communication systems in orbit using input power telemetry and output noise power.
The assignee of the present invention manufactures and deploys satellites carrying communication systems into geosynchronous and low earth orbits. Certain coverage patterns provided by communication systems produce many small spot beams. In many cases, the receive pattern and the transmit pattern are not over the same geographical location on the earth. Therefore, many payload test earth stations are required for payload testing while the satellite is in orbit.
In general, in-orbit testing of a satellite includes verifying the health of transponders and verifying the pointing and shape of the antenna patterns. Typically, these tests are end-to-end and require an earth station to provide an uplink and an earth station to receive and analyze the downlink signal. If the satellite's transmit and receive antenna patterns do not cover the same geographical location, two or more earth stations are required.
For satellites whose receive and transmit footprints cover essentially the same geographical area, (or if there are two earth stations, one in the receive and one in the transmit pattern), the antenna pattern verification is conducted by performing RF measurements while maneuvering the satellite through a set of attitude maneuvers. Saturated flux density (SFD) and Effective Isotropic Radiated Power (EIRP) at saturation are recorded along with satellite attitude telemetry, then analyzed, to determine the receive pattern and the transmit pattern. This method requires an uplink from an earth station and downlink reception at an earth station. This method is used throughout the industry.
For satellites whose receive and transmit footprints cover essentially the same geographical area (or if there are two earth stations, one in the receive and one in the transmit pattern), the health of the transponders is verified by executing transponder tests such as SFD/EIRP, power input versus power output, frequency response, etc. These test also require an uplink from an earth station and downlink reception at an earth station. This method is used throughout the industry.
For satellites that do not have an earth station in both the receive and transmit patterns, there are two known methods that achieve receive antenna pattern measurements in-orbit. One of these methods is used to measure receive antenna patterns of NSTARa and NSTARb satellites deployed by the assignee of the present invention, and the other is a method disclosed in U.S. Pat. No. 6,157,817. There is currently no method to achieve transmit antenna patterns for satellites unless both receive and transmit footprints are covered by earth stations. There is also no currently-available method to evaluate transponder health unless both receive and transmit footprints are covered by earth stations.
The NSTAR antenna pattern measurement method verifies a receive antenna pattern by recording signal strength telemetry resulting from an RF uplink at discrete attitude positions. The satellite attitude is commanded to a specified attitude position, an RF uplink test carrier is applied, the signal strength telemetry from an on board power sensing device is recorded, the uplink is removed, then the satellite attitude is commanded to the next attitude position. These steps are repeated until sufficient data is taken to analyze the RF pattern. The earth station that provides the RF test uplink is a geographically separate earth station from the earth station that provides command and telemetry.
In method disclosed in U.S. Pat. No. 6,157,817, the same earth station provides the RF test uplink and receives the telemetry. This presents a risk to the mission in the event the earth station becomes inoperable.
It would be desirable to have the capability of testing both the transponders and antenna patterns of a satellite-based communication systems without the requirement of having an earth station in both the receive and transmit footprints. This would allow for testing of the antenna patterns and transponders of multibeam satellites with a minimum number of earth stations. Accordingly, it is an objective of the present invention to provide for improved methods of testing multibeam satellite communication systems with a minimum of earth stations using input power telemetry and output noise power.